1. Field of the Invention
The present invention relates to an ophthalmic photography apparatus, and more particularly to an ophthalmic photography apparatus that can simultaneously photograph both the left and right images required for stereoscopic viewing of the fundus of an eye being examined.
2. Description of the Prior Art
With a conventional simultaneous stereoscopic fundus camera, as disclosed in Japanese Patent No. 2,642,417 and Japanese Patent No. 2,933,995, a two-aperture stop with two apertures (left and right) is provided at a position conjugate to the anterior ocular segment (conjugate to the pupil) of the eye being examined with respect to the objective lens, and each of the light beams from the fundus that pass through the two apertures is divided by a prism or the like into two optical paths, which are guided to a left-and-right pair of image-forming optical systems where separate images are formed in left and right regions of a film surface or the imaging surface of an imaging device, and then photographed.
In addition, Japanese Patent No. 3,255,730 discloses a configuration wherein the two apertures in the pupil-conjugate two-aperture stop are in the shape of a lengthwise rectangle, while Japanese Laid Open Patent Publication No. 1998-165372 describes a configuration wherein a cylindrical lens is used to cause images of the fundus to be alternately incident upon the pixels of the imaging device and thus photographed. Japanese Laid Open Patent Publication No. 1999-299739 further describes a configuration whereby the aperture stops at the fundus-conjugate position and the pupil-conjugate position are made variable, thereby permitting both stereoscopic and monocular photography to be performed with a single imaging medium.
Moreover, Japanese Laid Open Patent Publication Nos. 1997-18896 and 1997-211388 describe a configuration whereby alternating pixels of the imaging device are guided via a prism or the like to the left or right eye, respectively, thereby allowing the image to be viewed stereoscopically.
In addition, from Japanese Laid Open Patent Publication No. 2004-208744 is known an ophthalmic photography apparatus wherein the photographic stop that eliminates light reflected from the anterior ocular segment of the eye is moved in concert with the focusing lens while maintaining a position substantially conjugate to the anterior ocular segment of the eye being examined.
However, with the conventional configuration as disclosed in any of Japanese Patent Nos. 2,642,417, 2,933,995 or 3,255,730, it is necessary to dispose lenses for each of the left-and-right pair of image-forming optical systems separately for the two optical paths, making the configuration complex and causing the apparatus to become large and also more costly, and moreover there are problems in that the adjustment of the optics of the left and right optical paths becomes exceedingly complex and time-consuming.
In addition, with the configuration disclosed in Japanese Laid Open Patent Publication No. 1998-165372, the two images from the two-aperture stop (the left image and the right image) are alternately incident upon the pixels of the imaging device, but there are problems in that both the left image and the right image are incident upon a single pixel in the periphery of the imaging surface, and thus a good stereoscopic view is not obtained, for example.
In addition, in stereoscopic photography of the eye fundus, the difference of diopter of the eye being examined must be taken into consideration, so if the focusing lens is moved from the reference position to compensate for the difference in diopter of the eye being examined, there are problems in that the conjugate relationship between the position of the anterior ocular segment and the two-aperture stop is upset and also the light passing through the respective apertures of the two-aperture stop is no longer guided to the pixels of the imaging device in a regular manner.
Moreover, even if a two-aperture stop is disposed upon the image-side focal surface of the focusing lens and upon the object-side focal surface of the imaging lens to thereby constitute an image-side telecentric optical system, the system is indeed image-side telecentric for the normal diopter (zero diopter) with an accurate stereoscopic view guaranteed, but if the diopter shifts toward the plus side or the minus side, there is a problem wherein the optical system cannot be kept telecentric during focus adjustment, resulting in a stereoscopic view that becomes more concave or convex the nearer to the periphery of the imaging surface.